Thermal printers are becoming an increasingly popular form of commercial and home printing. Such printers require precise alignment of media relative to a printing head throughout a printing operation. However, as media is driven through a thermal printing operation, a possibility arises that the lateral location of the medium on the holder will be adjusted and that registration problems can arise. Even minor registration problems can create unacceptable image artifacts in an image formed by a thermal printer. Accordingly, what is needed is a low cost mechanism to ensure that rolled mediums such as thermal donor or receiver mediums maintain a constant position on during printing operations. Similar considerations arise in other forms of rolled medium printing.
One approach to solve this problem is found in the Shinko Electric Company's model CHC-S7045 printer. In this printer, a holder assembly has a first flange that is retained to a spring-loaded steel shaft and a second removable flange that is located at a fixed position on a threaded end of the steel shaft using a wing nut, which is also threaded onto the shaft. Once the wing nut is unthreaded, the removable flange can be slid off of the steel shaft allowing rolled media to be placed over the steel shaft and interface with the spring-loaded flange remaining on the shaft. The removable flange is re-installed over the steel shaft and the wing nut is threaded onto the steel shaft. The wing nut to removable flange is then tightened to a prefixed location with regard to the edge of the steel shaft creating a fixed dimension from the end of the shaft to the inside flange of the removable flange to thereby constrain the rolled medium.
It will be appreciated, however, and that such approach requires manual threading and provides a fixed structure that is expensive and time consuming to load.
Thus, what is needed is a low cost system for retaining rolled medium on a mandrel that allows quick replacement of the rolled medium and that provides dynamic constraints to the control the positioning of the rolled medium. What is also needed is an effective and inexpensive system for warning a user when a medium is not located properly thereon.